1. Field of the Invention
The present invention relates to a printing head. In particular, the present invention relates to a printing head, comprising a support member, being formed of a resin material, to which a printing element substrate of the printing head is bonded.
2. Description of the Related Art
A printing technique using an inkjet method has been known in terms of a low running cost and quiet printing method. In order to provide an inkjet printing apparatus at a lower price, it is effective to achieve a lower cost of a printing head for ejecting ink droplets that accounts for a high proportion of the total cost. A printing element substrate that is a chip for ejecting ink is accurately positioned in the surface of the printing head and bonded and secured thereto. In the printing head that has achieved a lower cost, the bonding surface, to which the printing element substrate is bonded and secured, often comprises a resin member. This is because the printing head can be produced at lower cost by use of an injection-molding technique than in case where the bonding surface of the printing element substrate comprises a member, for example, such as a ceramic member, other than the resin member.
Incidentally, in mounting a printing head to an inkjet printing apparatus, in order to ensure excellent printing quality, the dimension from the mounting reference surface to an orifice, through which ink is ejected, of a printing element substrate is required to be controlled and maintained accurately. For this reason, high flatness is needed for the bonding surface to which the printing element substrate is bonded. In order to achieve high flatness, it is preferable to keep the mold shrinkage factor of a molding resin uniform, and the thickness of the bonding surface (adhesion surface), to which the printing element substrate is adhered, comprising a resin member is required to be uniform as much as possible. Moreover, in achieving further cost reduction, for example, the shape of an ink flow passage for supplying ink to the printing element substrate and the shape of a mounting portion of a filter for removing dusts in ink are often formed from a supporting member comprising the same resin member. Accordingly, on the rear surface side of the bonding surface of a printing element substrate, a cavity portion for achieving uniform thickness is often provided (for example, see U.S. Pat. No. 7,063,411).
In a printing head having a cavity portion formed therein, an opening of the cavity portion is formed in a surface adjacent to the surface having the bonding surface and thus the strength of a portion proximate to the opening of the surface having the bonding portion is reduced.
Accordingly, for example, in mounting the printing head to the printing apparatus, if the printing head accidentally falls from an elevated place and the above-described portion having poor strength of the printing head receives an impact, the printing element substrate provided in the printing head may be damaged to cause printing failures.
As an example, with reference to FIG. 20 and FIG. 21, a printing head having a protruding portion H3560 on substantially the same plane as the bonding surface of a printing element substrate is described. FIG. 20 shows a state immediately before a printing head is fallen onto a floor, while FIG. 21 shows a state immediately after the printing head is fallen onto the floor. After the fallen printing head H3000 hits the floor, an impact from the floor is applied to the protruding portion H3560. Then, a bonding surface H3570, to which a printing element substrate H3100 is bonded, of a supporting member H3500 will be subjected to deformation due to the impact at the time of collision. Since the printing element substrate H3100 is bonded to the supporting member H3500 with an adhesive or the like, this deformation causes the printing element substrate H3100 to deform via the adhesive. Such deformation of the printing element substrate is undesirable because the deformation affects the printing quality.
Note that, in FIG. 20 and FIG. 21, a configuration has been described in which the protruding portion H3560 is formed on substantially the same plane as the bonding surface of the printing head. However, even in cases where the protruding portion H3560 is not formed in the printing head, an impact from the floor will transmit from a corner of the supporting member H3500 to the bonding surface H3570, thereby deforming the printing element substrate H3100, as with the above-described case.
Particularly, in cases where a rectangular ink supply port extending through the printing element substrate is provided in the printing element substrate, if the printing element substrate deforms due to an impact applied to the printing head, this deformation may have serious influence on the printing quality. This ink supply port is processed by anisotropic etching and has corner portions. Therefore, the deformation of the printing element substrate H3100 concentrates on a corner portion of the ink supply port. If this deformation becomes excessive, a crack may occur in the printing element substrate. A crack in the printing element substrate may disconnect wirings and the like inside the printing element substrate, causing printing failures.